The present invention concerns a process for producing coke and hydrocarbon distillate from hydrocarbonaceous oils. More specifically, the invention concerns a process for converting a heavy oil to provide a valuable liquid distillate and a high-purity coke by contacting the heavy oil with free oxygen and liquid phase water at an elevated temperature and pressure.
Heavy petroleum crude oils and heavy oil fractions such as residua may be used as low-grade commercial fuels. Heavy oils may also be converted to more valuable products by thermal or catalytic conversion processing. Such conventional conversion processes as delayed coking, fluid bed coking, catalytic cracking and hydrogen treating, with or without a catalyst, have been suggested for conversion of heavy oils. Heavy crudes and oil fractions often contain substantial concentrations of detrimental contaminants, including organic nitrogen and sulfur compounds, metals (especially nickel and vanadium), coke precursors (e.g., asphaltenes), and the like. When heavy oils are burned directly as fuel, the presence of metals, nitrogen and sulfur can result in contamination of flue gas with objectionable air pollutants including particulates, nitrogen oxides and sulfur oxides. In attempting to upgrade heavy oils by conventional catalytic processes, the presence in the oils of nitrogen, sulfur, and particularly nickel and vanadium, results in rapid deactivation of catalysts, and can cause catalytic upgrading of residual oils to be a less than completely satisfactory upgrading method.
When heavy crudes and oil fractions are subjected to conventional pyrolysis-type coking (e.g., delayed or fluid coking) at temperatures of 350.degree. C. to 500.degree. C., large concentrations of heat-sensitive, coke-forming materials, such as asphaltenes, can result in relatively low yields of the more valuable primary product, distillates, and relatively high yields of the less valuable by-product, coke. The presence of undesirably large concentrations of contaminants in coke derived by conventional coking of heavy oils detracts from the value of coke as a by-product. This is particularly true for sulfur. The quality of coke obtained from heavy oil high in contaminants may thus make it unsuitable for some uses, e.g., electrodes, because of poor specifications of such properties as coefficient of thermal expansion, electrical resistivity and sulfur content.
A general discussion of wet air oxidation technology, found in Mechanical Engineering, December 1979, page 30, is incorporated herein by specific reference. A discussion of regeneration of active carbon, after use in waste water treating, by means of wet air oxidation, found in AICHE Symposium Series, Vol. 76, No. 192, (Recent Advances in Separation Technology-II), Page 51, (AICHE, 1980), is incorporated herein by specific reference.
A process for removing pyritic sulfur from coal, by treatment with water and air at elevated temperature and pressure to convert the pyritic sulfur to water-soluble ferrous and ferric sulfate, is disclosed in U.S. Pat. No. 3,824,084. Use of silicates and an oxidizing agent (such as air, oxygen, hydrogen peroxide, alkali metal sulfides, alkaline earth metal sulfides) or a reducing agent (such as H.sub.2, CO, K.sub.2, S.sub.2 O.sub.4, NaS.sub.2 O.sub.4, and alkali metal polythionates) in an aqueous medium to desulfurize coal is disclosed in U.S. Pat. Nos. 4,174,953 and 4,197,090.
Use of wet air oxidation to provide heat energy in the form of steam, as by wet air oxidation of coal, is disclosed in U.S. Pat. Nos. 4,211,174, 4,100,730, and 4,013,560.
Use of copper or silver ions to catalyze wet air oxidation of organic material in waste water is disclosed in U.S. Pat. No. 3,912,626.
Treatment of papermill waste sludges by wet air oxidation to convert organic components to innocuous oxidation products and to provide for recovery of inorganic filter materials for reuse, is disclosed in U.S. Pat. No. 3,876,497.
Essentially complete oxidation of solid or liquid combustible materials which are difficult to suspend in water, such as diesel fuel and nitroglycerine, by direct injection into a wet air oxidation reactor, is disclosed in U.S. Pat. No. 4,174,280.
None of the publications concerning wet air oxidation is concerned with forming coke and distillate liquid from a hydrocarbonaceous oil. Hydrocarbonaceous materials which are utilized in the disclosed wet air oxidation systems are simply consumed to form highly oxidized waste materials, primarily carbon dioxide and water.